1. Field of the Invention
The present invention generally concerns communications interfaces, and in more particular concerns a scheme for interfacing a plurality of MAC interfaces to a single communications controller.
2. Background Information
The problem of interconnecting a number of physical (layer 1) or Media Access Control (MAC) (layer 2) communications interfaces to a single communications controller has been around for years. A number of standard interfaces have been developed to address this problem. These include Utopia1, Utopia2, and Utopia 3 (for ATM systems), and MII and RMII for IEEE802.3 systems. These systems tend to be physical layer or MAC layer dependent, and not well suited to route interfaces onboard an ASIC. For example, the Utopia interfaces only work for ATM cells, and use tristate buses. In addition, the RMII and MII interfaces do not multiplex data for many channels over a single set of wires, but require separate wires for each channel.
Because of these limitations, many ASIC designs that incorporate communications interfaces have tended to include internal ASIC buses with an address and a data bus and DMA (direct memory access) to supply the required functionality. The designs have then become very focused on the particular communications physical or MAC layer that is being utilized, and they have not been generally applicable to the breadth of communications interfaces that the industry uses. This leads to poor reusability of designs, and due to the tight coupling between the DMA engine and the communications interface, the ASIC design process leads to interdependencies between the two, such as routing sensitivity.